The invention relates generally to a fluid system having at least two different fluid circuits supplied in parallel by a common fluid source and, more particularly, to a pressure-compensated hydraulic system with regeneration, wherein the two parallel circuits have different loads that may be operated substantially simultaneously.
It is well known that when operating two different fluid circuits in parallel with a common pump, the circuit having the lightest load will automatically take the pump""s flow. Likewise, the circuit with the heaviest load will stall or slow to such an extent that the operation of that circuit is severely hampered. It is also desirable in many systems with a light load to recombine the flow from one end of a cylinder to the other end. However, this has proved to be difficult since it requires special valving in the main control spool or added valving. Even then, the functioning of the heavy loaded circuit would either slow or stall. In attempts to overcome the stalling of the heavy loaded circuit, excessive pressures may be generated in the fluid system.
In some systems, for example, U.S. Pat. No. 4,617,854, the hydraulic device includes a pump and at least two consumers fluidly connected to the pump, with each of the consumers being operatively controlled by a hydraulically-controlled multiway valve. In attempting to achieve load-independent proportioning, the device is provided with an additional hydraulically-controlled multiway valve acted upon by the pump pressure and the pressure of the consumer carrying the highest pressure. The additional multiway valve, as well as other multiway control valves are operated by the pump pressure. Such a system may not be desirable because it requires additional valving and it takes operative pressure from the pump flow.
The present invention is directed to overcoming one or more of the problems as set forth above.
According to one aspect of the invention, a fluid system may include a source of pressurized fluid in operable communication with first and second actuators. A first control valve may be operable to control fluid communication to and from the first actuator. The first control valve may be structured and arranged to combine fluid flow from a second end port of the first actuator with fluid flow from the source when providing a supply of fluid to a first end port of the first actuator. The first control valve may include a first signal port in fluid communication with the supply of fluid to the first actuator. A second control valve may be operable to control fluid communication to and from the second actuator. The second control valve may include a second signal port in fluid communication with a supply of fluid to the second actuator. A resolver may be structured and arranged to output a resolved signal pressure equal to the greater of a first signal pressure output by the first signal port and a second signal pressure output by a second signal port. A compensator in fluid communication with the first control valve and the first actuator may be structured and arranged to control fluid flow from first control valve to the first actuator based on the resolved signal pressure.
According to another aspect of the invention, a method for substantially simultaneously operating at least two actuators having different loads is provided. The method includes supplying pressurized fluid to a first control valve and to a second control valve, controlling fluid flow to and from the first actuator with the first control valve, and controlling fluid flow to and from the second actuator with the second control valve. The method further includes combining exhaust flow from a second end port of the first actuator with a supply of pressurized fluid to provide a fluid flow to the first actuator, outputting a first signal pressure from the first control valve, and outputting a second signal pressure from the second control valve. The method further includes comparing the first signal pressure with the second signal pressure and controlling fluid flow from the first control valve to the first actuator based on the greater of the first signal pressure and the second signal pressure.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention.